Binary mask side lobe suppression using space scattering bar

Use of off-axis illumination such as dipole and cross-pole to obtain minimum dense pitch resolution limits process margin due to side lobe defect pattern formation. Side lobe or ghost images are unwanted additional patterns formed at wafer image at certain pitch range where intensity drop occurs [I. Hur, Proc. SPIE 2440 (1995) 278], and there are limited ways in which ghost images can be reduced. One way to suppress ghost image is to use multi-pole illumination and such an illumination condition is difficult to generate using diffractive optic elements so a hard aperture must be used but its use limits throughput. An alternative way is to vary the mask phase in order to somewhat increase the intensity to alleviate the formation at certain pitch range [H. Iwasaki et al., Proc. SPIE 3236 (1997) 544]. But for patterning memory devices at and below 50 nm half-pitch, it is shown that binary mask provides beneficial results over attenuated phase shift mask due so called “mask induced polarization effect” [A. Estroff et al., Proc. SPIE 5754 (2005) 555; W.H. Cheng et al., Proc. SPIE 5992 (2005) 1; S. Teuber et al., Proc. SPIE 5754 (2005) 543; Y. Aksenov et al., Proc. SPIE 5754 (2005) 576; I. Höllein et al., Proc. SPIE 5853 (2005) 194]. Nevertheless, optical proximity corrections are to be performed and maximum obtainable process margin need to be obtained. Hence, a method of optimizing space scattering assist feature positioning and sizing is discussed in this paper. A simplified analysis method to optimize space scattering assist feature insertion is formulated for an optical proximity correction. A simplified model formulation is defined a priori, and its result is compared to results obtained from an empirically calibrated model and indicated a good correlation.